STREAMS/UX for the HP 9000 Reference Manual

Differences Between STREAMS/UX and System V Release 4 STREAMS

HP-UX Changes to Cloning

STREAMS/UX supports two methods of cloning. See the SVR4.2

STREAMS manual for more information about cloning. Some differences

exist between HP-UX cloning and SVR4.2 cloning.

The ﬁrst cloning method uses a special clone major number, 72, to provide

cloning. For each cloneable device, a device ﬁle must exist that has the

clone major number of 72 and also has a minor number equal to the major

number of the real device. When an application opens this type of device

ﬁle, STREAMS/UX passes the driver open routine CLONEOPEN in the

sﬂag parameter. The driver allocates a minor number and returns a new

device number containing the true major number and the chosen minor

number. The driver uses either makdev or to create the new device number.

The second cloning method is useful for drivers which need to be able to

encode information in their minor numbers. This is not possible in the ﬁrst

method, as the clone device ﬁle for that method must have as its minor

number the major number of the driver being cloned.

In the second cloning method, the driver designates a particular minor

number as its “clone” minor number. The driver open routine checks the

minor number portion of the device number parameter passed to it, and if it

is the clone minor number, the driver open routine allocates a minor number

and returns a new device number to the caller, in the same way as the ﬁrst

cloning method described above. The returned device number must contain

both a major number and the new minor number. A driver using this cloning

method may also change the major number in the device number it returns.

However, the new major number must correspond to a STREAMS/UX

driver with the same streamtab structure as the driver associated with the

original major number. Also, on a multiprocessor system, if the original

driver was MP scalable, the new one must be too. Likewise, if the original

was UP emulation, the new one must be also.